Early testing is the testing of inbreds for combining ability in the early stages of inbreeding, e. Therefore another mass selection after few years would be effective in improving the variety further. Introductions which require few years for adaptation are known as indirect introductions. However, it does not need to expend energy on attracting pollinators and can spread beyond areas where suitable pollinators can be found. By repeated selection desirable phenotypes, mixing the seeds, and growing them in each season to get a better composite variety. Selection is essentially based on the phenotype of plants. What is negative mass selection? Repeated inter-mating of heterozygous progeny provides greater opportunities for recombinations to occur.
This is done to avoid genetic variation in the experimental material so that the effects of treatments are easily detected. Wide adaptability and more flexibility to environmental changes due to heterozygosity and heterogenity. Examples of self-pollinating plants include wheat, barley, oats, rice, , apricots and peaches. At maturity the crop is harvested in mass, and the seeds are used to establish the next generation in a similar plot. A brief description of some commonly used chemicals of these groups is presented below. A brief description of these mutagens is presented below: Commonly used physical mutagens radiations , their properties and mode of action. Progeny selection is usually more effective than phenotypic selection when dealing with quantitative characters of low heritability.
They are generated from radioactive decay of some elements like 14C, 60Co, radium etc. In pedigree method, individual plants are selected from F2 and the subsequent generation and their progenies are tested. Why a cross between two clones exhibit segregation in F 1? The advantages of the backcross method are its rapidity, the small number of plants required, and the predictability of the outcome. A method to separate the inbreeding and selecting generations in order to speed the process along. Recurrent selection for specific combining ability. This method of selection will only be effective for highly heritable traits.
Fast and Thermal Neutrons D. Selfing the last backcross generation, coupled with selection, will give some progeny pure breeding for the genes being transferred. This completes the original cycle of selection. The correlated response in the unselected trait based on the selected trait indirect trait is higher than the direct response to selection of the unselected trait. At the end, single plant is selected and tested same as pedigree method. The introduced plant material can be used in following main ways: i It can be used directly as a variety. PowerPoint Presentation: For recurrent selection, several desirable plants are selected from the composited population obtained from the original selection cycle; they are selected on the basis of phenotype and are self-pollinated.
Either perfect or imperfect flowers Perfect flowers Dandelions use the wind to pollinate. What are main drawbacks of mass selection? The selfed seeds are harvested separately and saved for planting in the third year. This page includes main steps and detailed procedure for the development of pureline variety. This completes the first recurrent selection cycle. In cross pollinated crops, following breeding methods are used: i Plant introduction ii Mass and Progeny selection iii Heterosis breeding iv Synthetic breeding v Composite breeding vi Backcross method vii Polyploidy breeding viii Transgenic breeding ix Molecular breeding etc. A plant that does not conform to the requirements in any given year of the selection cycle is discarded from the program.
X-rays can break chromosomes and produce all types of mutations in nucleotides, viz. Single plant selections are then made and evaluated in the same way as in the pedigree method of breeding. The final evaluation of promising strains involves 1 observation, usually in a number of years and locations, to detect weaknesses that may not have appeared previously; 2 precise yield testing; and 3 quality testing. Selected plants are pollinated by both superior and inferior pollen parents. This evaluation is usually carried out in plots grown under conditions that simulate commercial planting practice as closely as possible. Half life is the function of temperature and pH for a particular compound. Pureline selection consists of following steps: i Selection of a heterogeneous material as base population.
Sonora 64 and Lerma Rojo Secondary introduction: Introduction that can be used as a variety after selection from the original genotype or used for transfer of some desirable gene to the cultivated variety Eg. These numbers illustrate the importance of efficient techniques in managing hybrid populations, for which purpose the pedigree procedure is most widely used. The second recurrent selection cycle may be initiated as in the case of the first recurrent selection cycle in the fourth year. A modern refinement of mass selection is to harvest the best plants separately and to grow and compare their progenies. A modern refinement of mass selection is to harvest the best plants separately and to grow and compare their progenies. What are examples of primary introduction? Since cross-pollinated species are naturally hybrid heterozygous for many traits and lose vigour as they become purebred homozygous , a goal of each of these breeding methods is to preserve or restore heterozygosity.
Thus the selection is based on the maternal parent only 2. For another selection type visit method. It should be noted that selection is now based not solely on the appearance of the parent plants but also on the appearance and performance of their progeny. Another term used for this method of is individual plant selection, as large numbers of plants are selected, but those are harvested individually, their individual progenies are grown and evaluated and then best progeny is released as a pureline variety. The double-cross procedure has the advantage that the commercial F1 seed is produced on the highly productive single cross A × B rather than on a poor-yielding inbred, thus reducing seed costs. When the number of families has been reduced to manageable proportions by visual selection, usually by the F7 or F8 generation, precise evaluation for performance and quality begins. Allows plant to be less resistant as a whole to disease.